1. Field of the Invention
The present invention relates to a refrigerating machine oil and a fluid composition for operating a refrigerating machine, more specifically a lubricant composition for a refrigerating machine employing a HFC-type refrigerant which contains at least one of HFC-32, HFC-125 and HFC-134a and using an ester having a specific structure alone or as a mixture of various types.
2. Discussion of Background
In recent years, by the problem of the depletion of ozone layer, CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) conventionally used as refrigerants for refrigerating machines, have been prohibited by regulations, and HFC (hydrofluorocarbon) has been used as a refrigerant instead of them. As a refrigerating machine oil for the HFC refrigerant, PAG (polyalkylene glycol), esters and the like which are compatible with HFC, have been studied or employed. For example, PAG is disclosed in U.S. Pat. No. 4,755,316, JP-A-1-198694, JP-A-1-256594, JP-A-1-259093, JP-A-1-259094, JP-A-1-259095, JP-A-1-274191, JP-A-2-43290, JP-A-2-55791 and JP-A-2-84491. The esters are disclosed in Japanese PCT publication No. 3-505602, JP-A-3-55791, JP-A-3-88892, JP-A-2-128991, JP-A-2-128992, JP-A-3-200895, JP-A-3-227397, JP-A-4-20597, JP-A-4-72390, JP-A-4-218592 and JP-A-4-218593. However, PAG has drawbacks of a high moisture adsorption and poor electrical insulating properties. On the other hand, ester oils may undergo hydrolysis and form an acid due to its structure, and the formed acid will be expected to cause various inconveniences in the refrigerating machine system. Further, these oils tend to be inferior in the lubricating properties to a conventional system of a mineral oil and CFC/HCFC or a conventional system of a mineral oil, an alkylbenzene and CFC/HCFC, whereby it has been studied to incorporate various additives thereto. The refrigerating machine oil is susceptible to the high temperature and high pressure atmosphere in a refrigerating compressor, or stains due to e.g. thermal decomposition of the refrigerating machine oil tend to attach within the compressor. These drawbacks bring about new problems. Under such circumstances, the present inventors have made extensive studies to improve the cleanness in the compressor, and as a result, found that the cleanness of various types of compressors can be improved by incorporating specific additives in specific amounts. They have accomplished the present invention based on the discovery.